Waveguides are widely used as laser amplifiers in optical systems. Waveguides consist of a high index core region encased between low index cladding regions. Waveguide lasers receive an input laser beam and amplify it to provide a higher power output beam. Amplification occurs in the core region, which is a gain medium that boosts the power of the input laser beam. The core region typically includes a matrix that incorporates an optical center (e.g. rare earth ion) that provides the gain. The matrix can be a crystalline or glass material and the optical center is introduced as a dopant. Crystalline materials include single crystals and ceramics. Representative crystalline gain media include oxide matrix materials (e.g. YAG, YVO4) doped with rare earths and representative glass gain media include oxide glass matrix materials (e.g. silica or modified silica) doped with rare earths.
Recent interest in high energy lasers has motivated efforts to develop waveguide lasers with sufficient gain to provide output powers of several tens of kilowatts up to a few megawatts. High gain can be achieved through high doping levels of the optical center that provides gain and/or by scaling up the size of the gain medium to increase the optical path length through the waveguide. Crystalline gain media typically permit higher doping levels than glass gain media, but are difficult to scale up in size and typically produce higher scattering losses than glass gain media. Optical centers such as rare earth ions typically have lower solubility and lower doping concentrations in glass gain media, but glass gain media are easier to scale up in size than crystalline gain media and exhibit lower scattering losses.
Efforts to develop waveguides based on crystalline gain media for high power laser applications have had limited success because of the difficulty in scaling up the size of crystalline materials and the long process times needed to produce large scale crystalline media. Glass gain media with large dimensions are available, but are expensive when made with existing manufacturing techniques. There is a need for a low cost method for producing glasses for waveguides.